The present invention relates to gas turbine engines, and more specifically to seals for use in turbine sections of gas turbine engines.
Gas turbine engines, such as those that power modern commercial and military aircraft, typically include a compressor to pressurize inflowing air, a combustor to burn a fuel in the presence of the pressurized air, and a turbine to extract energy from the resulting combustion gases. The turbine may include multiple rotatable blade arrays separated by multiple stationary vane arrays. A turbine blade array is typically situated radially within a blade outer air seal system or assembly (or “BOAS” system or assembly). In other words, a BOAS assembly may span an outer endwall between a plurality of static vane arrays situated upstream and downstream of the blade array. The BOAS assembly thus forms an outer (cylindrical) wall configured to confine a stream of hot post-combustion gases.
Cooling air is often provided to the BOAS assembly to enable operation while exposed to the hot combustion gases. This cooling air may be bled from one or more air compartments situated in proximity to the BOAS assembly and through one or more bleed apertures disposed within the BOAS assembly. A higher pressure is typically required to direct cooling air through the BOAS assembly. Effective seals may prevent leakage of cooling air between the BOAS assembly and adjacent component assemblies (e.g., vanes or vane arrays), thus allowing cooling air to flow within segments of the BOAS assembly.
As the turbine is heated by the combustor exhaust and pressurized, the cooling air may undesirably escape into the turbine through a variety of gaps between the BOAS assembly and adjacent vane arrays and other pathways formed as a result of thermal and maneuvering stresses placed upon the engine parts during operation. The thermal, mechanical and pressure induced deflections of individual components may require that some seals perform with substantial relative motion between sealing surfaces. More particularly, various BOAS assemblies may be capable of expanding and/or contracting in a radial direction to compensate for a radial motion of turbine blades or blade tips resulting from the forces placed upon the blades during operation (e.g., a maneuvering operation). Thus, seals are needed that will both allow relative movement between a BOAS assembly and adjacent vane arrays and minimize cooling air leakage between the BOAS and adjacent vane arrays. Minimizing cooling air leakage between the BOAS and the adjacent vane arrays can lead to improvements in gas turbine engine performance, such as improved flow output and increased fuel efficiency.